The present invention relates to a preparation for a transdermal drug administration that contains a local anesthetic as a medicinal ingredient.
Various preparations for transdermal administration of a local anesthetic, and some of them have been marketed as liquid- or ointment-form external preparations. However, application of these preparations to the common integument poses problems, such as difficulty in controlling the dose, possibility of staining clothes, and so on.
Although an analgesic composition, retains the drug at a local site longer (Japanese Patent Publication No. 130540/1988), such a composition falls within the category of liquid or ointment preparations intended for administration to mucous membrane, which is not entirely suitable for application to the common integument.
Japanese Patent Publication No. 272521/1989 teaches a patch preparation for application to the gum. This preparation overcomes disadvantages of conventional liquid or ointment preparations and can be handled easily. Still, this preparation is unsuitable for application to the common integument since it is originally designed for application to the gum; the application site must have adequate moisture in order to tightly secure the preparation to the site.
Also, an adhesive tape preparation for a transdermal administration of a local anesthetic (Japanese Patent Publication No. 299215/1989), offers easy application and easy control over the dose. Its self-adhesive matrix comprises an adhesive material selected from among the group of poly(styrene-butadiene) block copolymer, poly(styrene-isoprene-stylene) block copolymer, high molecular weight polyisobutylene polymer, low molecular weight polyisobutylene polymer and ethylene-vinyl acetate copolymer. Yet, such polymers or copolymers do not result in the rapid appearance of the anesthetic effect, which is one of the desired properties of a local anesthetic. Moreover, its self-adhesive matrix comprises an adhesion-imparting agent, a fluidity-imparting agent, and an antioxidant as a medicinal ingredients in addition to a local anesthetic. This is not only uneconomical, but also pharmaceutically unstable because of the potential reactions between those agents and the primary medicinal ingredient.
Japanese Patent Publication No. 185713/1985 teaches a preparation for transdermal drug administration in which a transdermally absorbable drug is dispersed as recrystallized fine powder in a pressure-sensitive adhesive macromolecule copolymer. This percutaneously absorbable drug is contained in an amount corresponding to at least 1.2 times the saturation solubility of the pressure-sensitive adhesive macromolecule copolymer. This preparation is easily handled and better controls the dose. Yet, according to the preparation's description, the amount of the transdermally absorbable drug relative to the pressure-sensitive adhesive macromolecule copolymer is 40 weight % or less, an amount that hinders a rapid anesthetic effect. For a rapid effect, it is necessary for the drug to be suddenly released or burst upon initial application; this drug release and the adhesion to the skin depend on the proportional amount of the dissolved drug to the undissolved drug in the pressure-sensitive adhesive macromolecule copolymer. However, this cited patent neither teaches or suggests this.